1. Technical Field of the Invention
The present invention relates to numerical control of machines. More particularly, the present invention relates to numerical control of machines, wherein a pivoting machine member is controllably propelled by one or more linear actuators.
2. Brief Description of the Related Art
Machines with pivoting members, particularly members for orienting a tool, and more particularly, a cutting tool, are well known. A conventional machine arrangement provides a spindle assembly for holding and rotating a cutting tool wherein the spindle assembly is provided relative to two (2) intersecting axes of rotation. Linear actuators propel the pivoting members to alter the orientation of the axis of rotation of the tool. Conventional numerical controls for such pivoting members provide position commands for the orientation specified in angular units, e.g., degrees or radians. However, the relationship between linear displacement of the propelling actuator and angular displacement of the machine member is non-linear. Hence, control of position of the propelling actuator in response to angular position commands must be effected through measurement of actual position of the pivoting member or through a non-linear position control algorithm.
It is conventional to control machine members with a servomechanism control implementing, at least, position and velocity control. In conventional systems, velocity commands are produced in response to differences between commanded and actual position, the magnitude of the position error defining the magnitude of the velocity command. To permit coordinated motion of multiple machine members, position commands are periodically generated, the magnitude of the position commands being a function of the rate of command generation and the commanded rate of motion of the machine members. Hence, to produce constant velocity, position commands defining displacements of equal magnitude are generated at a constant rate.
Because of the non-linear relationship between the linear displacement of the propelling actuator and the angular displacement of the pivoting member, the conventional control scheme will not result in the intended control velocity of the pivoting member absent a corresponding non-linear control algorithm, irrespective of whether position commands are generated in angular units defining orientation or linear units defining displacement of the propelling actuator. Hence, while measurement of actual actuator position of the pivoting machine member is satisfactory for servomechanism control of position, it is not satisfactory for servomechanism control of velocity to produce coordinated motion of machine members. However, conventional numerical controls do not provide such control algorithms.
It is an object of the present invention to provide control of pivoting machine members propelled by linear actuators to permit coordinated motion with translating machine members.
It is a further object of the present invention to provide control of pivoting machine members propelled by linear actuators wherein position measured for control of the pivoting member is displacement of the propelling actuator.
It is a further object of the present invention to provide control of pivoting machine members propelled by linear actuators wherein position commands for the pivoting machine members are given in angular units, measured position for control of the pivoting member is displacement of the propelling actuator, scaling is effected to match measured position units to command position units, and command position values are compensated to account for the non-linear relationship between displacement of the propelling actuator and orientation of the pivoting member.
These and additional objects, features and advantages of the present invention will become apparent to those reasonably skilled in the art from the description which follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the claims appended hereto.
In accordance with the aforesaid objects, the present invention provides control of pivoting machine members propelled by linear actuators so as to permit coordinated motion of the pivoting members with translating machine members. Position commands for the pivoting machine members are given in angular units. The propelling linear actuators are controlled by servomechanism control providing position and velocity control. Position measurements for the pivoting members measure linear displacement of the propelling actuator. Position commands for the pivoting members are compensated according to the non-linear relationship between displacement of the propelling actuator and the angular displacement of the pivoting member.